The purpose of this project is to investigate the tissue forces (tissue pressure, tissue colloid osmotic pressures) and lymph flow at different pulmonary capillary pressures. These physiological parameters will be measured in isolated dog and sheep lungs. In addition, histological and histochemical changes will be determined for each experimental condition. From this information, a tissue pressure volume curve can be constructed and we will be able to predict at what tissue pressure the alveolar membranes disrupt and intra-alveolar edema results. Also, lungs will be removed from animals with chronically elevated left atrial pressure. These lungs will be isolated and the same parameters will be determined. We will then evaluate as outlined above the changes that occur in the forces, flows, and structure in chronically elevated left atrial pressure animals.